Archaeolgists find carvings made by pre-Aztec civilisation

A stone block unearthed in Mexico and covered in carved patterns is thought to be the oldest example of writing found in the Americas.

Archaeologists believe the writing on the 26lb (12kg) block could date back to the first millennium BC. Road builders digging in a gravel quarry found the 14x8in (35x20cm) block at Cascajal, Veracruz. It is thought to be the work of the Olmec civilisation, which may have laid the foundations for the future Mayan and Aztec empires.

An international team of researchers, writing today in the journal Science, said that the find shed surprising new light on the Olmecs. The 62 symbols inscribed on the block contain distinct elements, repeated characters, and what appear to be sentences. Several paired sequences are suggestive of poetic couplets.

Dr Stephen Houston, of Brown University in Rhode Island, the co-author of the study, said: "It's a jaw-dropping find. It takes this civilisation to a different level."

Dr Houston, an expert on ancient writing, added: "This block shows a whole new dimension to the society and opens up the possibility that they could have kept records. It's telling us that these records probably exist and that many remain to be found. If we can decode their content, these earliest voices of Meso-American civilisation will speak to us today."

Meso-America is a region that extends from central Mexico to Costa Rica, and spawned a number of ancient cultures. The Olmec people appeared on the coast of the Gulf of Mexico around 1200 BC. They quickly flourished, becoming a sophisticated society which built monumental structures and left behind carved stone heads 8 feet tall.

But, until now, no one knew they were able to write. The meaning of what is written on the Cascajal block remains a mystery, and the text's influence on later writing systems is unclear.

The characters run horizontally, rather than vertically as in later Meso-American scripts. Dr Houston said that deciphering the script would require the Mexican equivalent of a Rosetta Stone - an ancient stone tablet, discovered in 1799, whose three scripts gave scholars the key to understanding Egyptian hieroglyphs.

When found, the Cascajal block was surrounded by ceramic fragments and broken stone artefacts. Along with other clues, these helped scientists date it to the "San Lorenzo" phase of Olmec culture ending around 900 BC - about 400 years before writing was thought to have first appeared in the West.

The surface of the block is concave, leading researchers to believe that symbols had repeatedly been carved on it and erased.This was an "unprecedented" discovery, said Dr Houston.